DESCRIPTION (applicant's description): Cytokinesis is a fundamental process in all dividing animal cells. However, the mechanisms that regulate and mediate the localized assembly of the F-actin contractile ring, its stable attachment to the cell cortex, and its coordinated disassembly are not known. We have identified mutations in 29 new genes required at different specific stages of cytokinesis during male meiosis in Drosophila. This mutant collection presents an unparalleled opportunity to elucidate the molecular mechanisms that mediate and regulate cytokinesis in animal cells. Assembly of the F-actin contractile ring requires james bond and at least eight other genes. frodo functions to maintain linkage between the constricting acto-myosin ring and anillin at the cell cortex. ftvs, fsco, fun, onr, and bns are required for both cytokinesis and polarized cell outgrowth during spermatid elongation, suggesting a common underlying mechanism. To investigate their stage and mode of action we will determine if the genes are required for assembly or localization of other contractile ring proteins, mid-spindle components, and key actin regulatory molecules such as CDC42 or Arp2/3 complex subunits. To investigate the common mechanism required for cytokinesis and flagellar elongation, we will determine if the fws, fsco, etc. mutations similarly affect F-actin assembly, disassembly, or reorganization or the localization of key actin-associated proteins during cytokinesis and at the tip of elongating spermatids. To elucidate molecular mechanisms of cytokinesis, we will clone selected genes, determine if their protein products are components of the contractile ring, central spindle, or spermatid flagella, test how their localization depends on wild type function of known cytokinesis genes and each other, and test whether they can bind anillin, septins, microtubules or actin, or bundle, sever, or cap microfilaments, or nucleate F-actin assembly in vitro.